JP2003103738A - Multi-layer polyimide film, polyimide laminate and polymer light guide path - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-layer polyimide film for a laminate which shows efficient film-forming properties without the generation of a breakage during forming a film and also outstanding release strength. SOLUTION: This multi-layer polyimide film is manufactured by superposing two kinds of polyamic acids in three layers while the acids are in the form of a solution and casting the melt over a support to obtain a self-supporting polyamic acid film and thermally imidating the film. In addition, the polyamic acid to be used for a center layer shows a specific coefficient of thermal expansion and a specific storage elastic modulus. Further, the polyamic acid to be used for both surface layers has a specific coefficient of thermal expansion and a specific glass transition temperature.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION The present invention is a multilayer polyimide film having excellent peel strength and having a thermal expansion coefficient close to that of a fluorinated polyimide, as well as having good film forming properties without causing breakage during film formation. When used as an optical waveguide substrate, there is no distortion between the waveguide portion and a polyimide laminate capable of obtaining a polymer optical waveguide with a small polarization dependent loss, and a high thermal expansion coefficient and excellent at 300 ° C. The present invention relates to a polymer optical waveguide exhibiting shape retention.

[0002]

2. Description of the Related Art Conventionally, as an optical waveguide, an inorganic optical waveguide in which a waveguide is formed by using quartz or the like on a silicon or glass substrate has been widely known.

However, while this inorganic optical waveguide has excellent properties such as low optical loss and high reliability, it requires heating at a temperature of several thousand degrees Celsius when the waveguide is formed, and thus requires a special device for manufacturing. However, there is a problem that not only the manufacturing cost is high, but also the degree of freedom of the manufacturing process is limited in the case of mixed mounting with electronic components.

On the other hand, in recent years, the development of organic optical waveguides using fluorinated polyimide in the waveguide portion has been advanced.

Although this organic optical waveguide has many advantages such as being able to be manufactured at a relatively low temperature of about 300 ° C.,
When a silicon substrate is used as the substrate for this organic optical waveguide, distortion occurs between the fluorinated polyimide having a very large thermal expansion coefficient and the silicon substrate, and the polarization-dependent loss is large due to this distortion. There was a problem of becoming.

[0006]

SUMMARY OF THE INVENTION The present invention has been achieved as a result of studying the solution of the above-mentioned problems in the prior art.

Therefore, an object of the present invention is that the film-forming property is good without causing breakage during film formation, and that it has a thermal expansion coefficient close to that of a multilayer polyimide film or fluorinated polyimide having excellent peel strength. When used as an optical waveguide substrate, there is no distortion between the waveguide portion and a polyimide laminate capable of obtaining a polymer optical waveguide with a small polarization dependent loss, and a high thermal expansion coefficient and excellent at 300 ° C. It is intended to provide a polymer optical waveguide exhibiting shape retention.

[0008]

In order to achieve the above-mentioned object, the multilayer polyimide film of the present invention is prepared by laminating two kinds of polyamic acids in a solution state in three layers and casting them on a support to self-coat them. After obtaining a supporting polyamic acid film, a multilayer polyimide film obtained by heating imidization of the polyamic acid,
The polyamic acid used for the central layer is a single layer and has a film thickness of 20 to 6
When formed on a polyimide film of 0 μm, the average value of the thermal expansion coefficient in the tensile mode of 50 ° C. to 200 ° C. is 50 ppm / ° C. or more, and the storage elastic modulus of 300 ° C. is 50 ° C. or less. 50% or more, and when the polyamic acid used for both surface layers covering this central layer is formed as a single layer into a polyimide film having a film thickness of 20 to 60 micrometers, in a tensile mode of 50 ° C to 200 ° C. Average thermal expansion coefficient of 50ppm / ℃
The glass transition temperature is 300 ° C. or lower.

In the multilayer polyimide film of the present invention, it is preferable that the polyamic acid used for the central layer has structural units represented by the following general formulas (I) and (II).

[0010]

[Chemical 5]

[0011]

[Chemical 6] [Wherein R3 is

[0012]

[Chemical 7] R4 is

[0013]

[Chemical 8] X is any one selected from the group represented by
The molar ratio of Y is 100 to 20: 0 to 80. ] Further, the polyimide multilayer laminate of the present invention is a polyimide laminate obtained by laminating any number of the above-mentioned multilayer polyimide films, heating, pressurization, 0.3 mm or more,
In particular, it is characterized by having a thickness of 0.4 mm or more and 0.7 mm or less and having an average value of the thermal expansion coefficient in the compression mode of 50 ° C. to 200 ° C. of 50 ppm / ° C. or more.

In the polyimide multi-layer laminate of the present invention, the outermost layer has an average coefficient of thermal expansion of 50 ppm / ° C. or higher and 300 in the tensile mode of 50 ° C. to 200 ° C.
A polyimide film having a storage elastic modulus at 50 ° C of 50% or more of the storage elastic modulus at 50 ° C was used, and the above-mentioned multilayer polyimide film was used for the other layers, and tensile elasticity was applied to any layer except the outermost layer. A preferable condition is that a thin plate having a rate of 2 Gpa or more is inserted.

Further, the polymer optical waveguide of the present invention is characterized by using the above-mentioned polyimide laminate as a substrate.

In the polymer optical waveguide of the present invention, the warp in the manufacturing process is 1 mm or less in the range of 50 mm in length, and the polarization dependent loss is 0.1 dB / at a wavelength of 1.3 μm. A preferable condition is that it is not more than cm.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.

The multilayer polyimide film of the present invention is characterized in that a thermoplastic polyimide and a non-thermoplastic polyimide are laminated at the stage of polyamic acid, and this is imidized. It is possible to obtain a more excellent peel strength as compared with the case where each of the plastic polyimides is prepared and heated and pressed to form a laminate.

Furthermore, when a thermoplastic polyimide and a non-thermoplastic polyimide are prepared, respectively, particularly when a single layer is formed into a polyimide film having a film thickness of 20 to 60 μm, a tensile mode of 50 ° C. to 200 ° C. is used. The non-thermoplastic polyimide having an average thermal expansion coefficient of 50 ppm / ° C or higher is very fragile and breaks at the stage of imidization of polyamic acid to polyimide, but it is obtained by the method of imidizing three layers of polyamic acid. In the obtained multilayer polyimide film of the present invention, since the surface layer acts as a buffer layer, the breakage of the central layer can be effectively prevented.

Further, in ordinary polyimide film formation, it is necessary to heat the polyamic acid at a high temperature exceeding 400 ° C. at the imidization stage, and it is not possible to form a thermoplastic polyimide film having a glass transition temperature of 300 ° C. or less. It is very difficult, but in the present invention, since the central layer is a non-thermoplastic polyimide, the shape is retained even when heated, and it is possible to easily perform film formation under good film formability. Is.

In order to exhibit the above-mentioned properties, the multilayer polyimide film of the present invention is a self-supporting polyamic acid film in which two kinds of polyamic acids are superposed in three layers in a solution state and cast on a support. A multi-layered polyimide film obtained by heat-imidizing the polyamic acid after obtaining, wherein the polyamic acid used for the central layer is formed as a single layer into a polyimide film having a thickness of 20 to 60 micrometers. In addition, the average value of the coefficient of thermal expansion in the tensile mode from 50 ° C to 200 ° C is 5
0ppm / ℃ or more and storage elastic modulus at 300 ℃ is 50 ℃
Is 50% or more of the storage elastic modulus, and the polyamic acid used for both surface layers covering the central layer has a film thickness of 20.
When formed into a polyimide film of -60 μm, it is essential that the average value of the thermal expansion coefficient in the tensile mode of 50 ° C. to 200 ° C. is 50 ppm / ° C. or higher and the glass transition temperature is 300 ° C. or lower. As a condition.

That is, in the multilayer polyimide film of the present invention, the central layer is a non-thermoplastic polyimide, both surface layers are thermoplastic polyimide, and 50 of each layer.
It is important that the average value of the coefficient of thermal expansion in the tensile mode from 0 ° C to 200 ° C, the storage elastic modulus of 300 ° C and the glass transition temperature are within the specific ranges.

The polyamic acid solution used in the present invention is obtained by polymerizing at least one diamine component and at least one tetracarboxylic dianhydride.

As a method for polymerizing the polyamic acid solution,
After the diamine compound is placed in the solvent, one or more tetracarboxylic dianhydrides are added to the reaction components in an amount of 95 to 105
After mixing at a ratio of mol% for a time necessary for the reaction, a diamine compound is further added, and subsequently, one or more tetracarboxylic dianhydrides are mixed with all the diamine components and all the tetracarboxylic dianhydride components. A method of adding and polymerizing so as to be an equal amount, and after putting one or more kinds of tetracarboxylic dianhydride in a solvent, the diamine compound is reacted at a ratio of 95 to 105 mol% with respect to the reaction components. After mixing for a required time, one or more tetracarboxylic acid dianhydrides are added, and then a diamine compound is added so that the total diamine component and the one or more tetracarboxylic acid dianhydride components are approximately equal in amount. And a method of polymerizing the same.

Here, the polyamic acid used as the central layer preferably has structural units represented by the following general formulas (I) and (II).

[0026]

[Chemical 9]

[0027]

[Chemical 10] [However, in the formula, R5 is

[0028]

[Chemical 11] R6 is

[0029]

[Chemical 12] X is any one selected from the group represented by
The molar ratio of Y is 100 to 20: 0 to 80. ] Specific examples of the polyamic acid used in this central layer include diaminodiphenyl ether, 1,3 bis- (4 aminophenoxy) benzene, and 2,2-bis [4- (4-
Aminophenoxy) phenyl] propane, 4,4'-bis (4-aminophenoxy) biphenyl, 1,4-bis (4-aminophenoxy) benzene, phenylenediamine and other diamine components, and pyromellitic dianhydride. Representative pyromellitic acids or pyromellitic acids and 3,3′-4,4′-biphenyltetracarboxylic acid or dianhydride thereof, or 3,3′-4,4′-benzophenonetetracarboxylic acid or dianhydride thereof And 4,4′-oxydiphthalic acid or a tetracarboxylic acid compound having two or more benzene rings such as a dianhydride thereof, which is obtained by polymerizing in a solvent, and produces a non-thermoplastic polyimide. To be

Specific examples of the polyamic acid used for both surface layers include diaminodiphenyl ether, 1,
3bis- (4aminophenoxy) benzene, 2,2-bis [4- (4-aminophenoxy) phenyl] propane,
4,4'-bis (4-aminophenoxy) biphenyl,
Diamine components such as 1,4-bis (4-aminophenoxy) benzene and phenylenediamine, and pyromellitic acid represented by pyromellitic dianhydride or 3,
3'-4,4'-biphenyltetracarboxylic acid or its dianhydride, 3,3'-4,4'-benzophenonetetracarboxylic acid or its dianhydride, 4,4'-oxydiphthalic acid or its dianhydride And a tetracarboxylic acid compound having two or more benzene rings are polymerized in a solvent to form a thermoplastic polyimide.

As the solvent used in the above polymerization, dimethyl sulfoxide, N, N-dimethylacetamide,
Examples thereof include N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, N-methyl-2-pyrrolidone and dimethyl sulfone, and these are preferably used alone or in combination.

The polyamic acid obtained by the above polymerization is
It is adjusted to be 10 to 30% by weight in the solvent.

Next, a method for obtaining a multilayer polyimide film from the obtained polyamic acid solution will be described.

First, by using a co-extrusion die or the like capable of laminating three kinds of polymers in arbitrary thicknesses, a polyamic acid which forms the above-mentioned non-thermoplastic polyimide is used as a central layer, and a polyamic acid which forms the above-mentioned thermoplastic polyimide is formed. A three-layer polyamic acid solution is cast on a support and used for both surface layers to obtain a self-supporting polyamic acid film. Then, the obtained polyamic acid film is fixed to a metal frame with a pin and heat-treated at a temperature of 200 ° C. to 700 ° C. to obtain a multilayer polyimide film.

In the above, the support means glass,
It means a metal, a polymer film or the like having a flat surface and capable of supporting the cast polyamic acid when the polyamic acid is cast thereon.

Further, in the above, casting means spreading a polyamic acid on a support. Examples of casting include bar coating, spin coating, or a method in which a polyamic acid is extruded from a pipe-shaped substance having an arbitrary hollow shape and spread on a support.

When the obtained polyamic acid is cyclized into a polyimide film, it may be carried out by either a chemical ring-closing method of dehydrating using a dehydrating agent and a catalyst or a thermal ring-closing method of thermally dehydrating. The multilayer polyimide film obtained by using the thermal cyclization method has a high thermal expansion coefficient, and when used as a substrate for an optical waveguide, distortion with the core is reduced, which is preferable.

Examples of the dehydrating agent used in the chemical ring-closing method include aliphatic acid anhydrides such as acetic anhydride and acid anhydrides such as phthalic anhydride. These are preferably used alone or in combination. . As the catalyst, pyridine,
Heterocyclic tertiary amines such as picoline and quinoline, aliphatic tertiary amines such as triethylamine, N, N-
Examples thereof include tertiary amines such as dimethylaniline, and it is preferable to use these alone or in combination.

The multi-layer polyimide film of the present invention thus constructed has good film-forming properties without causing breakage during film-forming and has excellent peel strength.

Therefore, the polyimide laminate of the present invention obtained by laminating an arbitrary number of the above-mentioned multilayer polyimide films, heating and pressurizing, is 0.3 mm or more, particularly 0.4 m.
The average value of the thermal expansion coefficient in the compression mode from 50 ° C. to 200 ° C. when the thickness is m or more and 0.7 mm or less is 50 pp
It exhibits excellent characteristics of m / ° C or higher.

In the polyimide laminate of the present invention, the outermost layer has an average thermal expansion coefficient of 50 ppm / ° C. or more in a tensile mode of 50 ° C. to 200 ° C. and a storage elastic modulus of 300 ° C. of 50 ° C. A single-layer polyimide film having a rate of 50% or more can be used, and the above-mentioned multi-layer polyimide film can be used for the other layers. It can be expected to exhibit an excellent effect of preventing the adhesion.

In the polyimide laminate of the present invention, the tensile elastic modulus is 2 Gp in any layer except the outermost layer.
Sheets that are a or larger, such as Kapton (R) HA, Kapton (R) E
N (Kapton is a registered trademark of DuPont), a stainless steel plate, or the like can be inserted, and in this case, it is expected that the excellent effect of preventing warpage during the production of the optical waveguide can be exhibited.

Since the polyimide laminate of the present invention having the above structure has a thermal expansion coefficient close to that of fluorinated polyimide, when used as an optical waveguide substrate, there is no distortion with the waveguide portion and polarization dependence. A polymer optical waveguide with low loss can be obtained.

The polarization-dependent loss here means the difference between the optical loss of polarized light parallel to the waveguide surface and the optical loss of polarized light perpendicular to the waveguide surface.

Therefore, the polymer optical waveguide of the present invention using the above-mentioned polyimide laminate as a substrate has a warp in the manufacturing process of 1 mm or less within a range of 50 mm in length and a polarization dependent loss at a wavelength of 1.3 μm. 0.1 dB / c
Demonstrating excellent performance of m or less, optical communication connector,
It can be suitably used for applications such as photoelectric conversion elements.

[0046]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

In the above and the following embodiments,
Glass transition temperature (Tg) is DVE-V of Rheology Co.
4, a driving frequency of 110 Hz, a temperature rising rate of 2 ° C./min,
It is the temperature of the maximum value of the loss tangent when the vibration displacement is 16 μm.

The coefficient of thermal expansion is 50 ° C. by using a thermomechanical analyzer TMA50 manufactured by Shimadzu Corporation.
It is a value when an average thermal expansion coefficient of 200 ° C. is measured.

Reference Example 1 10 equipped with a DC stirrer
In a 00 ml separable flask, 1,3 bis- (4 aminophenoxy) benzene 41.68 (143 mmo
l), 58.53 g (143 mmol) of 2,2-bis [4- (4-aminophenoxy) phenyl] propane, and 608.37 g of N, N′-dimethylacetamide were added, and the mixture was stirred at room temperature under a nitrogen atmosphere. 1 after 30 minutes
60.33 g of pyromellitic dianhydride over time
(277 mmol) was added in several times. further,
After stirring for 1 hour, pyromellitic dianhydride / N, N '
-31.0 g of dimethylacetamide solution (6 wt%) was added dropwise over 30 minutes, and the mixture was further stirred for 1 hour. The viscosity of the polyamic acid obtained here was 2500 poise.

A part of the obtained polyamic acid was taken on a polyester film and a uniform film was formed using a spin coater. This was heated and dried in an oven at 100 ° C. for 1 hour to obtain a self-supporting polyamic acid film.

The obtained polyamic acid film was fixed to a metal frame with a pin and heated at 200 ° C. for 30 minutes and 300 ° C. for 20 minutes.
Heat treatment was performed at 400 ° C. for 5 minutes to obtain a polyimide film.

Table 1 summarizes the polyimide films obtained and the number of films torn during the heat treatment. 50 ° C to 200 ° C of the obtained polyimide film (thickness: 50 μm)
Average value of thermal expansion coefficient is 57.5p
pm / ° C., elongation at break was 6%. Further 300 ℃
Had a storage elastic modulus of 2.34 GPa, which was 66% of the storage elastic modulus at 50 ° C, that is, 3.53 GPa.

Reference Example 2 50 equipped with a DC stirrer
In a 0 ml separable flask, 1,3 bis- (4-aminophenoxy) benzene 34.542 (118 mmo
l), N, N'-dimethylacetamide 258.867
g, and stirred at room temperature under a nitrogen atmosphere. From 30 minutes to 1 hour later, 29.32 g (95 mmol) of 4,4'-oxydiphthalic acid dianhydride was added in several times. After stirring for 1 hour, pyromellitic dianhydride 4.
38 g (20 mmol) was added in several times. After stirring for 1 hour, pyromellitic dianhydride / N,
N'-dimethylacetamide solution (6 wt%) 12.8
g was added dropwise over 30 minutes, and the mixture was further stirred for 1 hour.

The viscosity of the polyamic acid obtained here is 2
It was 000 poise.

A part of the obtained polyamic acid was taken on a polyester film, and a uniform film was formed using a spin coater. This was heated and dried in an oven at 100 ° C. for 1 hour to obtain a self-supporting polyamic acid film.

The obtained polyamic acid film was fixed to a metal frame with a pin and held at 200 ° C. for 30 minutes and 300 ° C. for 20 minutes.
A polyimide film was obtained by heat treatment at 00 ° C. for 5 minutes.

Table 1 shows the numbers of the polyimide films obtained and the films torn during the heat treatment. 50 ° C to 200 ° C of the obtained polyimide film (thickness: 25 μm)
The average value of the coefficient of thermal expansion in the tensile mode of 60.0p
It was pm / ° C. About the obtained polyimide film, using DVE-V4 of Rheology, drive frequency 11
The glass transition temperature (Tg) measured at 0 Hz, a temperature rising rate of 2 ° C./min, and a vibration displacement of 16 μm was 246 ° C.

[Example 1] Using a coextrusion die capable of laminating three kinds of polymers in arbitrary thicknesses, the polyamic acid obtained in Reference Example 1 was used as a central layer and the polyamic acid obtained in Reference Example 2 was used as a core layer. The three-layer polyamic acid solution used for the surface layer was cast on a support and heated and dried to obtain a self-supporting polyamic acid film.

The obtained polyamic acid film was fixed to a metal frame with a pin, and the temperature was 200 ° C. for 30 minutes and 300 ° C. for 20 minutes.
Heat treatment was performed at 400 ° C. for 5 minutes to obtain a multilayer polyimide film.

Table 1 summarizes the number of the obtained multi-layer polyimide films and the films torn during the heat treatment. As a result of observation with a polarization microscope, the thickness of each layer of the obtained multilayer polyimide film (thickness: 65 μm) was 10/45/10.
(Μm), the elongation at break was 9%.

[0061]

[Table 1] [Example 2] Multilayer polyimide film 8 obtained in Example 1
Overlapping, 200 ℃, 120 minutes 0Kg / c
A polyimide laminate was prepared by thermocompression bonding at 40 kg / cm ² at m ² , 375 ° C. for 60 minutes. The peel strength of the central layer is 90 °, and the crosshead speed is 50 mm /
It was measured at min and the results are summarized in Table 2. The average value of the coefficient of thermal expansion in the compressed mode was 65.0 ppm / ° C.

Example 3 On a disc-shaped laminate having a diameter of 10.16 cm, made of the polyimide laminate obtained in Example 1,
An embedded fluorinated polyimide optical waveguide was prepared using a fluorinated polyimide material for an optical waveguide having a core / clad refractive index difference of 0.6%.

First, a fluorinated polyamic acid solution for clad was spin-coated on the polyimide laminate, and this was coated with 3
The lower clad layer was formed by imidization by heating at 00 ° C. or higher. Next, a fluorinated polyamic acid solution for core was spin-coated on this, and this was heated and imidized at 300 ° C. or higher to form a core layer. Then, a linear core pattern was formed on the core layer using an aluminum mask and a photoresist, and a core ridge was formed by dry etching with oxygen gas. Finally, a fluorinated polyamic acid solution for cladding was spin-coated on the etched core, and this was heated and imidized at 300 ° C. or higher to form an upper cladding layer. In this way, a linear optical waveguide having a width of 10 mm and a length of 50 mm was cut out from the embedded fluorinated polyimide optical waveguide formed on the disc-shaped laminate having a diameter of 10.16 cm.

The warp of this linear optical waveguide has a length of 50 mm.
Was less than 1 mm. In addition, the polarization dependent loss when light with a wavelength of 1.3 micrometers was guided through this polymer optical waveguide was 0.1 dB / cm or less.

[Comparative Example 1] Nine polyimide films obtained in Reference Example 1 and eight polyimide films obtained in Reference Example 2 were alternately laminated, and 200 ° C, 120 minutes, 0 Kg / c
A polyimide laminate was prepared by thermocompression bonding at 40 kg / cm ² at m ² , 375 ° C. for 60 minutes. The peel strength of the central layer is 90 °, and the crosshead speed is 50 mm /
The measurement was performed under the condition of min, and the results are summarized in Table 2.

[0066]

[Table 2]

[0067]

As described above, the multilayer polyimide film of the present invention has good film-forming properties without causing breakage during film-forming and has excellent peel strength.

Further, since the polyimide laminate of the present invention obtained by laminating an arbitrary number of the above-mentioned multilayer polyimide films, heating and pressurizing it has a thermal expansion coefficient close to that of fluorinated polyimide, it was used as an optical waveguide substrate. In this case, it is possible to obtain a polymer optical waveguide with no distortion between the waveguide portion and the polarization dependent loss.

Furthermore, the polymer optical waveguide of the present invention using the above-mentioned polyimide laminate as a substrate has a high coefficient of thermal expansion and 30
It exhibits excellent shape retention at 0 ° C.

Continued front page    (72) Inventor Hirokazu Yokoyama             6 Toray De, 31-31 Shintakaracho, Tokai City, Aichi Prefecture             TUPON CORPORATION Tokai Plant (72) Inventor Toru Matsuura             2-1-1, Nishishinjuku, Shinjuku-ku, Tokyo             Nutty Advance Technology Co., Ltd.             Inside the company (72) Inventor Fumio Yamamoto             2-1-1, Nishishinjuku, Shinjuku-ku, Tokyo             Nutty Advance Technology Co., Ltd.             Inside the company (72) Inventor Shigekuni Sasaki             2-1-1, Nishishinjuku, Shinjuku-ku, Tokyo             Nutty Advance Technology Co., Ltd.             Inside the company F-term (reference) 2H047 KA02 PA28 QA05                 4F100 AK49A AK49B AK49C AK49D                       BA03 BA04 BA10A BA10C                       BA25B EJ423 JA02A JA02B                       JA02C JA05A JA05C JK02D                       JK07B JK07D YY00A YY00B                       YY00C YY00D                 4J043 PA04 QB31 TA14 TA22 UA121                       UA122 UA131 UA132 UA141                       UA151 UB122 VA021 VA022                       VA031 VA062 YA06 ZB47

Claims (9)

[Claims] 1. A method of stacking two kinds of polyamic acids in a solution state in three layers and casting them on a support to obtain a self-supporting polyamic acid film, and then subjecting the polyamic acid to thermal imidization. In the resulting multilayer polyimide film, when the polyamic acid used for the central layer is formed as a single layer into a polyimide film having a film thickness of 20 to 60 micrometers, the thermal expansion coefficient in a tensile mode of 50 ° C to 200 ° C. Average value of 50ppm /
The storage elastic modulus at 30 ° C or higher and at 50 ° C is 50% or more of the storage elastic modulus at 50 ° C, and the polyamic acid used for both surface layers covering the central layer is a single layer having a thickness of 20 to 60 μm. When formed into a polyimide film,
The average value of the thermal expansion coefficient in the tensile mode of 50 ° C to 200 ° C is 50 ppm / ° C or more, and the glass transition temperature is 3
A multilayer polyimide film having a temperature of 00 ° C. or lower. 2. The polyamic acid used for the central layer is
The multilayer polyimide film according to claim 1, which has structural units represented by the following general formulas (I) and (II). [Chemical 1] [Chemical 2] [However, in the formula, R1 is R2 is [Chemical 4] X is any one selected from the group represented by
The molar ratio of Y is 100 to 20: 0 to 80. ] 3. A polyimide laminate obtained by laminating an arbitrary number of multilayer polyimide films according to claim 1 or 2 and heating and pressurizing the laminate, which has a thickness of 0.3 mm or more and from 50 ° C. An average value of the coefficient of thermal expansion in a compression mode of 200 ° C. is 50 ppm / ° C. or more, a polyimide laminate. 4. A polyimide laminate obtained by laminating an arbitrary number of the multilayer polyimide films according to claim 1 or 2 and heating and pressurizing the laminated polyimide film, which has a thickness of 0.4 mm or more and 0.7 or more.
A polyimide laminate having a thickness of mm or less and an average value of thermal expansion coefficients in a compression mode of 50 ° C. to 200 ° C. of 50 ppm / ° C. or more. 5. The outermost layer has an average thermal expansion coefficient of 50 ppm / ° C. or more in a tensile mode of 50 ° C. to 200 ° C. and a storage elastic modulus of 300 ° C. of 50% or more of a storage elastic modulus of 50 ° C. The polyimide laminate according to claim 3 or 4, wherein a certain polyimide film is used, and the multilayer polyimide film according to claim 1 or 2 is used for the other layers. 6. The polyimide laminate according to claim 5, wherein a thin plate having a tensile elastic modulus of 2 Gpa or more is inserted in any layer other than the outermost layer of the polyimide laminate. 7. A polymer optical waveguide comprising the polyimide laminate according to claim 3 as a substrate. 8. The polymer optical waveguide according to claim 7, wherein the warp during the manufacturing process is 1 mm or less within a length of 50 mm. 9. The polymer optical waveguide according to claim 7, wherein the polarization dependent loss is 0.1 dB / cm or less at a wavelength of 1.3 μm.